What is experimental psychology?

Wilhelm Wundt, answered from the texts and cited to the page.

Wilhelm Wundt answers

Psychology became a science the moment it acquired a method equal to its subject — and that method is experiment. Let me say precisely what this means, because the word is abused. The old introspective school — the Herbartians above all — claimed to observe the mind directly, by pure inner attention, and to report what they found. The result was that if one offered a prize for a single undisputed fact produced by this whole school, it would go unclaimed.¹

Their compendia multiply; students are burdened with imaginary processes presented as observed ones; and the representatives of the subjective method hold radically divergent opinions on hardly any question of fact they touch.² This is not science. It is metaphysics wearing the costume of observation. What experiment introduces is control. Psychical experiences are, in themselves, indeterminate magnitudes — they cannot be treated exactly until they have been referred to determinate units of measurement standing in constant causal relations with other given magnitudes.³

The experimental modification of consciousness by external stimuli provides precisely this: it subjects mental processes to arbitrarily determined conditions, which we may keep constant or vary as we will.⁴ The moment of observation is fixed, the stimulus is measurable, the procedure is repeatable. This is what makes introspection reliable — not the abolition of inner observation, but its binding to controllable outer conditions.

There is a further reason, peculiar to psychology and absent from natural science. The very intention to observe modifies the psychical process under observation, or suppresses it entirely.⁵ Pure introspection cannot escape this; it disturbs what it examines. Only by producing the process through a known external stimulus — a tone-vibration, a light-impression — can we study it under conditions favorable for observation, because we know what we have set going and when.⁶

The scope of experimental psychology is, accordingly, the whole of individual psychology: directly, where the experimental method applies; indirectly, where its general results and the refinement of observation it induces can be brought to bear on processes not directly accessible to external modification.⁷ But it has a boundary, and I have always marked it.

The higher mental processes — language, myth, the products of collective life across generations — arise under conditions no laboratory can produce or vary. For these, a second method is required: the historical and comparative study of general mental products. Psychology has, like natural science, two exact methods, and a psychology that possesses only the first has only the lower half of its subject.⁸

Sources

1. It has been well said that if a prize were offered for the discovery by this whole introspective school of one single undisputed fact, it would be offered in vain.

   Principles of Physiological Psychology Vol I

2. it is certain that the subjective method has no success to boast of; for there is hardly a single question of fact upon which its representatives do not hold radically divergent opinions.

   Principles of Physiological Psychology Vol I

3. Our psychical experiences are, primarily, indeterminate magnitudes; they are incapable of exact treatment until they have been referred to determinate units of measurement, which in turn may be brought into constant causal relations with other given magnitudes.

   Principles of Physiological Psychology Vol I

4. Modification from without enables us to subject our mental processes to arbitrarily determined conditions, over which we have complete control, and which we may keep constant or vary as we will.

   Principles of Physiological Psychology Vol I

5. the very intention to observe, which is a necessary condition of all observation, modifies essentially the rise and progress of psychical processes.

   Outlines of Psychology

6. A sensation arises in us under the most favorable conditions for observation when it is caused by an external sense-stimulus, as, for example, a tone-sensation from an external tone-vibration, or a light-sensation from an external light-impression.

   Outlines of Psychology

7. We now understand by 'experimental psychology' not simply those portions of psychology which are directly accessible to experimentation, but the whole of individual psychology. For all such psychology employs the experimental method: directly, where its direct use is possible; but in all other cases indirectly, by availing itself of the general results which the direct employment of the method has yielded.

   Principles of Physiological Psychology Vol I

8. Thus psychology has, like natural science, two exact methods: the experimental method, serving for the analysis of simpler psychical processes, and the observation of general mental products, serving for the investigation of the higher psychical processes and developments.

   Outlines of Psychology